Bugs in interface.py

[bastikr]

Hi all,
There are some bugs in interface.py:
  * All methods raise "NotImplemented" instead of "NotImplementedError()"
  * There are two methods called "retreieve" instead of "retrieve"
Since these interfaces are not defined as abstract base classes these bugs are not really relevant but it won't hurt to fix them.

 - Sebastian

p.s.: Please let me know if I should make patch.
p.s. 2: Branch with fixes at github: http://github.com/bastikr/python-puremvc/tree/master/trunk/

[puremvc]

@bastikr Thanks for pointing these out (and offering the fixes). And for the Python 3 port.

Toby, can you see about putting these fixes in first, then I'll do a branch for Python 2x and we can upgrade the trunk with the Python 3 changes?

Thanks,
-=Cliff>